Journal of Applied Physiology, Vol 76, Issue 4 1636-1642, Copyright © 1994 by American Physiological Society
L-carnitine combined with minimal electrical stimulation promotes type transformation of canine latissimus dorsi
M. L. Dubelaar, J. F. Glatz, Y. F. De Jong, F. H. Van der Veen and W. C. Hulsmann
Department of Physiology, Cardiovascular Research Institute Maastricht, University of Limburg, The Netherlands.
In the first part of this study, in four dogs the left latissimus dorsi was
equipped to perform in vivo contraction measurements and the right
latissimus dorsi served as control. After a control period, the dogs
received L-carnitine intravenously for 8 wk. We found that carnitine caused
the percentage of type I fibers to increase from 30 to 55% in the left
latissimus dorsi but no change in the right latissimus dorsi. In the left
latissimus dorsi, the contraction speed (percentage ripple) decreased from
75 to 30% and cytochrome-c oxidase activity increased 1.6-fold. No changes
occurred in the right latissimus dorsi. To verify these observations, we
performed a second study with placebo control for 8 wk, and only the left
latissimus dorsi was subjected to weekly electrical stimulation. In the
carnitine-treated dogs, the stimulated muscle showed an increase in the
percentage of type I fibers from 16 to 35% and the ripple decreased from 92
to 77%. These measures did not change in the placebo-treated dogs. We
concluded that weekly short-term stimulation does not lead to a change in
fiber type; however, carnitine combined with minimal stimulation of the
muscle leads to a significant shift in muscle fiber type composition toward
a muscle with an increased content of type I fibers.
